1. Field of the Invention
This invention relates generally to substrate handling and coating systems, and more particularly to a novel dual mode step and dwell or pass-through design for the construction of a sputtering machine apparatus for coating computer memory media, and including a cylindrical shaped vacuum chamber and apparatus for the holding, transporting, heating, cooling, and coating of a multiplicity of disk substrates.
2. Brief Description of the Prior Art
Hard disk drives provide fast, non-volatile, rewritable and economical computer memory. Virtually all disk media, such as magnetic hard disks, magneto-optical disks and phase-change optical disks, involve coatings by various physical deposition techniques such as sputtering or chemical deposition. Currently, the computer memory disk media industry utilizes two general types of sputtering machines for the sputter-deposition of a succession of various layers onto the disk surfaces to produce the memory media.
The first type of sputtering machine is an in-line or "pass-through" machine. It consists of either a linear arrangement of relatively small individual but connected chambers, or one or two long chambers with vacuum transition locks at each end of the line. Processing stations are located either along the long chambers or at each individual chamber. During deposition, a multiple-disk substrate carrier, called a pallet, continuously passes in front of the sputtering targets or sources. U.S. Pat. No. 4,894,133, issued to Hedgcoth and entitled "Method and Apparatus for Making Magnetic Recording Disk." describes such an in-line machine. Another example is taught by U.S. Pat. No. 4,749,465, issued to Flint et al. and entitled "In-Line Disk Sputtering System." This machine uses a massive block with a semi-circular groove rather than the conventional pallet to hold the disks. Still another example of this type of machine is taught by U.S. Pat. No. 3,290,670, issued to Charschan et al. and entitled "Apparatus for Processing Materials in a Controlled Atmosphere." Vendors of large machines of this type include Ulvac of Japan, Leybold of Germany, and Wilder Associates (formally Circuit Processing Apparatus) of the USA. In addition, some companies custom build their own large in-line machines for in-house use.
A second type of sputtering machine is a stationary or "static deposition" machine. In these machines, a single disk substrate moves in succession from one processing station to the next, where various processing steps, such as heating, sputtering and cooling, take place while the substrate remains fixed with respect to the processing source (hence the terminology "static machine"). Typically, the processing stations in static systems are arranged along a circular path so that the disk input (loading) and output (unloading) stations are adjacent to each other. Such is the layout of the machine taught in U.S. Pat. No. 5,425,611, issued to Hughes et al. and entitled "Substrate Handling and Processing System." The Intevac MDP-250 memory disk sputtering system made by Intevac is another example of a static system. Of similar layout is another commercial machine, the Circulus 12 built by Balzers/Leybold. Yet another example of a static machine adopting a folded linear design is described in U.S. Pat. No. 4,500,407, issued to Boys and entitled "Disk or Wafer Handling and Coating System." This machine also has the input and output stations adjacent to each other. An exception is the in-line static machine offered by Ulvac, where a pallet carrying several disks stops in front of a group of individual sputtering targets (or sources) each facing a disk in the pallet.
None of the above-described sputtering machines fully satisfies the requirements for the mass production of high-quality hard disks or wafers. The first-mentioned type of machines have relatively high throughput but usually produce excessive debris and defects in the coated disks. Such contamination debris arise from several sources. One source is attributable to the entrance vacuum lock, where rapid pumping of the load-lock stirs the air violently, causing transfer of small particles of debris from the pallet and the chamber interior to the surface of the disks. The debris particles are generally knocked off the disks by after-coating buffing and/or burnishing, leaving defects in the magnetic memory layer and other layers.
A second source of particulate debris in pass-through machines is the vibrational motion of the disks in the pallet as the pallet moves through the machine. Since the pallet makes many passes through the machine before cleaning, a relatively thick layer of coating gradually builds up on the pallet. The stress in the films builds up with thickness. The combined film stress, thermal cycling and abrasive action between the disk edge and the pallet holder lead to shedding of particulate debris. Some shedding of debris at the disk holder may also occur upon loading the disk onto the pallet; such shedding may occur even if sophisticated robots are used. The pallet-related debris also lead to defects in the layers including the magnetic memory layer.
Arcing or spitting in the carbon overcoat deposition station presents another source of magnetic defects. Most of today's hard disks use hydrogenated carbon (also called diamond-like carbon or DLC) as the overcoat or protective layer. Unlike electrically conductive graphite, hydrogenated carbon is a dielectric. It builds up an insulating layer on various areas of the sputtering target, causing sporadic arcing. The arc-accelerated particles can penetrate the magnetic memory layer and produce memory defects. Although this problem may be minimized by reducing the power supplied to the sputtering target, this also decreases the carbon sputtering rate and accordingly reduces the machine throughput. A better solution to the arcing problem involves the use of a high temperature substrate and a different, e.g., silicon carbide (SiC), overcoat in lieu of the conventional hydrogenated carbon overcoat. However, the SiC sputter-deposition is normally conducted at an elevated temperature, i.e., 700.degree. C. or above to obtain the necessary crystalline structure. Most of the current machines of the first-mentioned type use aluminum pallets that tend to warp, soften or even melt at elevated temperatures. Other pallet materials with higher melting points could be used, but the cost would be prohibitively high.
A static machine carries a single disk at a time sequentially from one processing station to the next. Because no pallet is used, the shedding of debris is greatly reduced, and the process temperature may be higher than that in a typical pass-through machine. As a result, such machines generally produce disks with fewer magnetic defects and debris contamination compared with a pass-through machine. However, these machines have their own drawbacks. First, the one-disk-at-a-time processing in a typical static machine causes its throughput to be two to four times lower than that of a typical pass-through machine. In addition, unless a pass-through machine can be made totally compatible with high-temperature processing, as described in detail below, the problem of arcing during carbon deposition will persist, making it practically impossible to raise the throughput of the machine by simply raising the power to the sputtering target. Finally, because the equipment costs of the two types of machines are similar, the per-disk manufacturing cost for a static machine is generally noticeably higher than that for a pass-through machine. In short, because future magnetic hard disk drives, with higher packing densities, will command low-cost disks with extremely low defects, there is an urgent need to raise the throughput of a static machine to the level of a pass-through machine without sacrificing quality or cost.
Current magnetic disk sputtering machines have several additional limitations. One of the most severe limitations is that they generally are not compatible with high-temperature processing dictated by newly developed, advanced substrate and coating materials. Currently, most magnetic hard disk substrates comprise non-magnetic nickel phosphorus plated aluminum (NiP/Al). This substrate cannot be heated above approximately 300.degree. C. due to phase segregation in the NiP, which renders it magnetic and, therefore, useless. Also, the NiP/Al substrates begin to warp and deform long before the aluminum melting point of 660.degree. C. is reached. Development work has been done on alternative substrate materials, e.g., silicon carbide, glass and ceramics, and on alternative overcoat materials, e.g., silicon carbide. Future disk coating machines must be compatible with these new materials.
A first issue in connection with this high-temperature compatibility problem is that heating devices in current magnetic disk sputtering machines are often not designed for rapid high-temperature processing. To maintain the throughput of the machine, it is desirable to have new heating devices that will rapidly heat up disks to the processing temperatures and, in particular, to the high processing temperatures (e.g., 1000.degree. C.) dictated by the aforesaid advanced substrate and coating materials in approximately the same length of time as for heating NiP/Al substrates in current machines. Additionally, it is desirable that the new heating device has improved substrate thermal isolation so that most of the thermal energy will go to the substrate but not its surroundings.
A second issue in connection with the aforementioned compatibility problem is that cooling methods and devices in current magnetic disk sputtering machines are often not designed for rapid cooling, either. The hydrogen content in the hydrogenated carbon film decreases as the substrate temperature increases. To possess certain desirable tribological properties, the hydrogenated carbon film preferably contains a certain amount of hydrogen. Hence, to ensure proper hydrogen content in the sputtered carbon film, substrates must be cooled in special cooling stations prior to the carbon deposition. This additional step will slow down the process unless it is efficient. Various prior art methods have been used for cooling substrates in evacuated chambers. One example is U.S. Pat. No. 4,909,314, issued to Lamont, Jr. and entitled "Apparatus for Thermal Treatment of a Wafer in an Evacuated Environment," which teaches a near-contact heat exchanging body configured in the shape of the article to be cooled. The surface of the article and the heat exchanging surface are not in intimate thermal contact. Rather, a conductive gas at a pressure significantly higher than that in the vacuum chamber but significantly lower than the atmospheric pressure is introduced between the two surfaces to fill the voids and improve the heat exchange between them. Another example is U.S. Pat. No. 5,287,914, issued to Hughes and entitled "System for Substrate Cooling in an Evacuated Environment," which teaches a stationary cooling system for thin substrates. This system employs a space or gap between the heat exchanger and the substrate. A highly conductive gas (e.g., helium) at a pressure of a few torr is introduced into the space to cool the substrate surface through both conduction and convection. However, even a highly heat-conductive gas is not a good heat conductor in comparison to most solids. Convective gaseous heat transport at such relative low pressures is not very effective, either. As a result, neither of these devices provides sufficient cooling for substrates. As a specific example, in the Hughes method above, the cooling rates across the 0.05 to 0.25 inch gap are only about 150.degree. C. per minute under ideal conditions. In a high-throughput disk coating machine, substrates are typically transported to the next processing station every 10 seconds or less. This means that substrates can only be cooled by about 25.degree. C. at a single cooling station. Furthermore, many new substrates, e.g., silicon carbide, are processed at temperatures above 700.degree. C. Therefore, to maintain the throughput of the machine, it is desirable to have new cooling devices that will cool down the disks more rapidly, particularly if high-temperature processing is involved.
Another limitation of typical current magnetic disk sputtering machines is that their process monitoring and control methods and setups are often either ineffective or overly complicated. To allow rapid detection and correction of problems associated with each of the processes, so that the overall product yield can be improved, there is a need for a simple yet effective process monitoring and control system that can be built into essentially all of the processing stations of a coating machine.
Yet another limitation of typical current magnetic disk sputtering machines is that their substrate holders do not meet the requirements of a high-quality, high-throughput coating machine. Typically, a disk in a static machine seats in the holder by gravity. To allow for rapid acceleration and deceleration associated with faster disk transport from one processing station to the next, disks need to be supported more solidly in the machine without merely relying upon gravity to seat them into the holders. In addition, the holder and shields must work together to confine the coating flux to the substrate and minimize coating of the holder, so that flaking of particulate debris from the holder can be reduced. An improved substrate holder should also be operable at elevated temperatures, e.g., 1000.degree. C., to permit processing of advanced substrate and coating materials described above.
In addition to the problem of holding and heating the substrate, there is an increasing demand within the disk drive industry to coat the disk uniformly to its extreme outer edge. The current art in disk substrate manufacturing and coating does not permit a totally acceptable solution to the problem. An improved substrate holder and coating system should also provide a unique and easily implemented solution to the problem of coating the disk substrate uniformly to its extreme outer edge.
A further limitation of typical current magnetic disk sputtering machines is that their sputtering magnetrons are not optimally designed for coating either single or multiple substrates. Planar sputtering magnetrons using permanent magnets have been used in the prior art, mostly for coating from a variety of electrically conductive targets. For example, U.S. Pat. No. 5,262,028, issued to Manley and entitled "Planar Magnetron Sputtering Magnet Assembly," teaches both circular and rectangular planar magnetron designs, whose improved magnetic pole-piece structures and magnet placement allow much better utilization of the target material. Another example is U.S. Pat. No. 4,818,358, issued to Hubert et al. and entitled "Magnetron Cathode Sputter Coating Apparatus," teaches the use of an arrangement of oriented magnets to form two curved racetracks on a rectangular planar magnetron. Other prior art shown in U.S. Pat. No. 4,865,708 to Welty, U.S. Pat. No. 4,964,968 to Arita, and U.S. Pat. No. 5,415,754 to Manley as well as application PCT/US92/00722 to Hollars et al also concentrate on designs for improved utilization of target material. For the circular planar magnetrons used to coat a single disk substrate in static mode, this improvement in target utilization actually causes non-uniform coating thickness and non-uniform coating properties on the disk. It is, therefore, desirable to have an improved circular planar magnetron which provides uniform coatings and coating properties, and an improved rectangular type magnetron for coating in the passthrough mode which is powered by a single power supply, and allows the simultaneous processing of a multiplicity of disk or wafer substrates at a given processing station.
All of the patents mentioned above are hereby incorporated by reference for purposes of additional disclosure.